I have PDF2 customisation built that is used from within an Oxygen 19.0 project
(the publication of manuals is done by the revising author right after approval from his authoring environment)

I have the customisation directory set up outside the DITA-OT and Oxygen environment,
that contains all of our local branding stuff and code (includes artwork, vars and index files)

Now I need a variant on this customisation, specialising only a few templates and the paper size
For that I have a new customisation directory in the same package, with a different scenario from the same project

I have tried two things
- using a nextCatalog in the variant catalog.xml to refer to the base brand customisation
- import both the custom xslt of the base brand customisation at the level of the variant customisation (and do the same with the font catalog)
Both options work reasonably well

BUT
I can't seem to find a way to make the variant customisation pick up the artwork and var files from the base customisation
and an elegant way to pick up the index references from the base catalog

Currently I have an exact copy of vars, indexes and artwork in
The reference to the "common" seems hardcoded in code at a level I don't want to mess with in the customisation

I need to control the entire application from a single project directory.
Portability is way more important than avoiding the vars duplication
Still it would make my development efforts way more robust if I only had a single copy of the vars and indexes

Any good ideas I am missing?
Thanks

Geert

PS: having multiple DITA OT scenarios on the project level, it would be nice if I could make the common plugin scenarios invisible to my users.
Can that be done too?

I'm not sure how best to handle this. You could try to register and ask around on the DITA Users List, the Oxygen forum is more static and mostly we, the Oxygen developers are notified when somebody posts a new topic.
For example you could have two separate customization folders with duplicate files in them. And have a custom ANT build file which synchronizes them, for example it copies the resources from one customization folder to another. So that whenever you make changes to one of them you can run the custom ANT build file and synchronize the other folder to contain the changes.

About your Oxygen-related question:

PS: having multiple DITA OT scenarios on the project level, it would be nice if I could make the common plugin scenarios invisible to my users.
Can that be done too?

Yes, but not by directly saving those scenarios at project level.
In the Oxygen Preferences->"Document Types Associations" page there is a "DITA Map" framework configuration, that framework configuration is the one which defines those default transformation scenarios. You need to extend that framework customization and save the extension at project level.
In the same "Document Type Association" page there is a "Project options" radio button at the bottom of the page.
Switch to project options, then use the "Extend" button to extend the "DITA Map" framework configuration, make changes to its "Transformation" tab (for example remove the default scenarios and add your own) and save the extension by clicking apply/ok in all dialogs.
Once you do that, whenever you open a DITA Map your custom framework extension saved at project level will be used to customize it and provide the transformation scenarios for it.
End users will see those custom transformation scenarios as read-only which might also be a bonus, they will need to duplicate the scenarios if they want to make changes to them.